1. Field of the Invention
The present invention relates to a liquid ejection apparatus, and more particularly, to a liquid ejection apparatus and control technology for a liquid ejection head suitable for same, which ejects liquid onto an ejection receiving medium by using a liquid ejection head having pressure generating elements corresponding to a plurality of nozzles.
2. Description of the Related Art
In general, in an inkjet recording apparatus, ink droplets are ejected at prescribed timings, respectively, from a plurality of nozzles of a head, on the basis of the dot pattern data (also called “dot data” or “print data”) developed from image data for printing which has been input from a host computer, and printing is carried out by means of these ink droplets landing on and adhering to a medium, such as recording paper.
In particular, in single-pass recording in which an image is recorded by means of a single relative scanning action on a medium by a line head having a nozzle row of a length corresponding to the breadthways direction of the medium, there are nozzles that frequently perform ink ejection, and nozzles that hardly perform ink ejection, at respective locations within the head. In the nozzles that hardly perform ink ejection, a viscosity change (viscosity increase) occurs in the ink inside these nozzles, and it becomes difficult to eject ink from the nozzles. In order to avoid problems of this kind, methods have been proposed whereby ejection is controlled in such a manner that the drive signals for the piezoelectric elements are varied in accordance with external conditions (environmental conditions) and ejection conditions (ejection state), and the ink temperature is measured and the ink temperature inside the head is controlled by a heater on the basis of the measured temperature, so that it remains uniform.
Japanese Patent Application Publication No. 10-193597 discloses an inkjet recording head having a plurality of channels which are mutually parallel and separated by partitions of piezoelectric ceramic, in which the partitions are caused to deform by means of a drive voltage, thereby causing the ink filled in the channels to be ejected selectively from the nozzles. Electrical heating bodies are provided in recess sections formed extending in a substantially perpendicular direction to the channels, on the reverse side of the piezoelectric ceramic partitions from the side adjacent to the channels. The ink filled in the channels is kept to a prescribed temperature by means of the electrical heating bodies.
However, in cases where various functions are imparted to the ink, or where it is sought to achieve high performance in the ink, the viscosity of the ink often increases. When ejecting high-viscosity ink of this kind, a drive signal having a waveform with a high drive voltage, sharp rise and sharp fall is required, compared to a case where an ink of general viscosity (lower viscosity than high-function, high-performance ink) is ejected. Consequently, the drive circuit for the ejection elements must be compatible with high-voltage and high-current operation, while at the same time, it must also be compatible with a short ejection cycle (high ejection frequency), which has an inverse relationship with high voltage and current.
In a head having a very large number of nozzles, such as a line head, even if the drive signals to be supplied to the piezoelectric elements are adjusted in accordance with the external environment, there is a possibility that locally situated nozzles having low ejection frequencies are not suitably cared. This situation is particularly notable in the case of high-viscosity ink which has a higher viscosity than generally used ink. Moreover, when the drive signals are adjusted in accordance with the ejection conditions, then not only does the ejection control procedure become complicated, but also, the scale of the wiring which transmits the drive signals and the scale of the drive circuit for generating the drive signals increases. Furthermore, if a heater and a temperature measurement sensor are provided for each nozzle, then there is a problem in that the head, the heater drive circuit and the sensor circuits all increase in size. When seeking to achieve high-speed through-put, as in a line head, then if the response of the temperature sensors is poor, it takes time to measure the temperature and satisfactory temperature control may not be possible.
In the inkjet recording head described in Japanese Patent Application Publication No. 10-193597, it is difficult to arrange the nozzles two-dimensionally, and there are limitations on increasing the nozzle density.